Hydraulic transmission devices for elimination of deterioration of the seal gasket of hydraulic pump pistons



Feb. 4, 1964 G. ALFIERI HYDRAULIC TRANSMISSION DEVICES FOR ELIMINATION OF DETERIORATION OF THE SEAL GASKET OF HYDRAULIC PUMP PISTONS Filed Nov 22, 1961 United States Patent HYDRAULHI TRANSMESION DEVICES FOR ELIMINATION OF DETERIORATION 0F TEE SEAL GASKET 0F HYDRAULIC PUMP PHSTGNS Giuseppe Ah'ieri, Milan, Italy, assignor to Fabbrica itaihrna Magueii Marelli S.p.A., Milan, Italy, an Italian joint-stock company Filed Nov. 22, 1961, Ser. No. 154,153 Claims priority, application italy Dec. 16, 1960 2 Claims. (Cl. 6i 54.5)

The present invention relates to hydrodynamic transmission devices of the type having a piston-type pump and hydraulic receiver adapted to eliminate wear of a seal gasket associated with the pump piston.

it is known that, in the devices of this type which may be used for servo controls, losses in pipes and connections between the pump and the receiver and thermal volume variations in the operating fiuid are compensated through a small hole that communicates the hydraulic circuit with a fluid tank when the piston of me pump is in rest position.

The presence of this small hole, however, causes deterioration of the pump piston seal gasket at the area of the gasket that closes the feed hole during the first part of the piston stroke. This is due principally to the pressure exercised by the fluid on the gasket, whereby the latter is pressed strongly against the wall of the cylinder.

The substantial value of the pressure is due to the fact that in the receiver cylinder the fluid acts immediately on the operating member.

In some cases, the hole is replaced With valves positioned before the rest position of the piston and mechanically opened by the piston itself in the last part or" its run towards the rest position. The hole may also be replaced with check valves efiective after the full run of the piston. The use of such valves, however, remarkably reduces the efiiciency of the pump.

An object of the present invention is to provide an improvement of the receiver cylinder, allowing the use of a small feed hole for communication between a tank and hydraulic circuit without causing the above mentioned deficiencies.

In substance, the invention is characterized by the fact that the transmission of control to the operating member or members is obtained by means of a receiver member submitted to the action of the feed fluid and at least one elastic return element, the assembly being arranged so that, in rest position, the hydraulic receiver member, due to the effect of the elastic return element is spaced by the operator member or members at a distance not less than to the run that the pump piston should effect, in order that the gasket may go beyond the feed hole While during the initial step of the run, the abovementioned distance may be reduced or eliminated by the effect of light pressure of the fluid.

The elastic return element may be connected with the receiver member; and it preferably consists of a spring.

Purely for exemplary purposes and not in a limiting sense, the sole figure of the accompanying drawing shows in section, an improved hydro-dynamic transmission member according to the invention, wherein P and R indicate respectively the pump and the hydraulic receiver. The pump and receiver being connected by a duct C.

The chamber 1 of the pump, in the rest condition of the 3,120,104 Patented Feb. 4, 1964 latter, is in communication with a tank 2 through a feed hole or opening 3 that is flush with the front face 4 of a radially expansible gasket 4 of a piston 5 against which a return spring 6, resting against cylinder bottom 7, acts.

Within a receiver cylinder 8 is a piston 9, adapted for sliding movement and furnished with the seal gasket iii. The piston is socket shaped in order to hold an extremely flexible spring 11 between the said piston and an associated operating member 12.

The spring may be supported in place with a pre-load that is sufficient merely to return the piston 9 to an initial rest position. During the operating step, the said piston compresses the spring 11 and after a stroke run S equal or slightly larger than the stroke S effected by the pump piston, contacts the operating member '12 so that further displacement of piston will cause corresponding displacement of member 12.

Tins allows the pump piston gasket 4 to pass the hole 3 while it is subject to insignificant hydraulic pressure and therefore gasket 4- is compressed against the wall of the cylinder 7 with a limited thrust due to bore arrangement B in such a way that it does not cause deterioration of the gasket.

After the initial run of the piston 9, owing to the reaction of element 12 there is strong pressure of fluid in 1 and therefore a corresponding collapsing of the gasket 4- also against the cylinder. The gasket, however, is not worn since it is then located past the hole 3.

It is understood that other practical embodiments of the invention may differ from that now described but without lying outside the scope of the invention. Thus for example, the spring can be mounted between two opposite plates, sockets or retainer cups of the piston and operating member. Furthermore, reference is made to a cylindrical return spring, which of course may be of a diiierent type.

What is claimed is:

1. Apparatus comprising a hydraulic pump comprising a cylinder and a piston reciprocable in said cylinder and defining a fluid chamber in the cylinder, a receiver coupled to said chamber and adapted for being operated by hydraulic forces originating in the chamber due to movement of said piston, a fluid supply, said cylinder being rovided with an opening coupling said chamber to said supply, a radially expansible gasket on the piston and adapted to seal fluid in said chamber, said gasket moving across said opening during movement of said piston, said piston being provided with a bore arrangement enabling expansion of said gasket under the influence of fluid pressure in the said chamber, a spring in said chamber in engagement with the piston to urge said piston to a position whereby said supply is in communication with said chamber, said piston having a stroke whereby said gasket is adapted to isolate said chamber from said supply, ad a lost-motion elastic means in said receiver to prevent substantial hydraulic pressure increases in said chamber until a determinable magnitude of movement of the said piston at which the gasket has moved past said opening whereby to avoid deterioration of said gasket, said receiver comprising a cylinder and a piston therein defining a chamber in which said elastic means is positioned, the latter said piston being operated by the pump piston through the intermediary of said elastic means, the elastic means comprising a piston and a spring effective between the latter said piston and the receiver piston to space the same by a distance enabling said gasket to travel past said opening before pressure in the pump chamber is increased by virtue of engagement between the pistons of the receiver and elastic means.

2. The combination defined in claim' 1 wherein the A spring the pump chamber normally maintains the gasket 5 at a distance from said opening which is less than the distance normally maintained between the pistons of the receiver and elastic rneans.

, References Cited in the file of this patent UNITED STATES PATENTS Chard Mar. 11, 1941 Baldwin Oct. 8, 1957 Baldwin Apr. 22, 1958 FOREIGN PATENTS France Q June 2, 1954 

1. APPARATUS COMPRISING A HYDRAULIC PUMP COMPRISING A CYLINDER AND A PISTON RECIPROCABLE IN SAID CYLINDER AND DEFINING A FLUID CHAMBER IN THE CYLINDER, A RECEIVER COUPLED TO SAID CHAMBER AND ADAPTED FOR BEING OPERATED BY HYDRAULIC FORCES ORIGINATING IN THE CHAMBER DUE TO MOVEMENT OF SAID PISTON, A FLUID SUPPLY, SAID CYLINDER BEING PROVIDED WITH AN OPENING COUPLING SAID CHAMBER TO SAID SUPPLY, A RADIALLY EXPANSIBLE GASKET ON THE PISTON AND ADAPTED TO SEAL FLUID IN SAID CHAMBER, SAID GASKET MOVING ACROSS SAID OPENING DURING MOVEMENT OF SAID PISTON, SAID PISTON BEING PROVIDED WITH A BORE ARRANGEMENT ENABLING EXPANSION OF SAID GASKET UNDER THE INFLUENCE OF FLUID PRESSURE IN THE SAID CHAMBER, A SPRING IN SAID CHAMBER IN ENGAGEMENT WITH THE PISTON TO URGE SAID PISTON TO A POSITION WHEREBY SAID SUPPLY IS IN COMMUNICATION WITH SAID CHAMBER, SAID PISTON HAVING A STROKE WHEREBY SAID GASKET IS ADAPTED TO ISOLATE SAID CHAMBER FROM SAID SUPPLY, AND A LOST-MOTION ELASTIC MEANS IN SAID RECEIVER TO PREVENT SUBSTANTIAL HYDRAULIC PRESSURE INCREASES IN SAID CHAMBER UNTIL A DETERMINABLE MAGNITUDE OF MOVEMENT OF THE SAID PISTON AT WHICH THE GASKET HAS MOVED PAST SAID OPENING WHEREBY TO AVOID DETERIORATION OF SAID GASKET, SAID RECEIVER COMPRISING A CYLINDER AND A PISTON THEREIN DEFINING A CHAMBER IN WHICH SAID ELASTIC MEANS IS POSITIONED, THE LATTER SAID PISTON BEING OPERATED BY THE PUMP PISTON THROUGH THE INTERMEDIARY OF SAID ELASTIC MEANS, THE ELASTIC MEANS COMPRISING A PISTON AND A SPRING EFFECTIVE BETWEEN THE LATTER SAID PISTON AND THE RECEIVER PISTON TO SPACE THE SAME BY A DISTANCE ENABLING SAID GASKET TO TRAVEL PAST SAID OPENING BEFORE PRESSURE IN THE PUMP CHAMBER IS INCREASED BY VIRTUE OF ENGAGEMENT BETWEEN THE PISTONS OF THE RECEIVER AND ELASTIC MEANS. 